As electromagnetic operating devices for various electromagnetic operated valves such as a directional controll valve, a proportional control valve, etc., there are known various types of electromechanical transducers for respectively exerting a mechanical output on a valve element against a spring force. For the electromagnetic operated valves, an electromagnet device using a solenoid coil, generally, an electromagnetic plunger device called a solenoid device has been widely used, and contrivances for economizing power consumption and making size and weight reductions have heretofore been proposed in various ways.
In this type of solenoid device, an iron core structure made principally of a fixed core, a movable core, and a yoke is equipped with a solenoid coil. Magnetic fluxes produced from the excited solenoid coil pass through a magnetic path formed by the iron core structure, so that the movable core forming an air gap in the magnetic path with respect to the fixed core is magnetically attracted to the fixed core. A mechanical output based on the displacement of the movable core at this time is transmitted to the valve element through, for example, a push rod or a coil spring.
Various experiments and studies for speeding up the operation of the electromagnetic operated valve employed for such a solenoid device to thereby improve the responsiveness have heretofore been performed. However, most of them relate to selection of the design specifications of coils small in electrical time constant (λ=L/R) and the design of coils for providing a correspondence to driving at a relatively high power supply voltage, and it's no exaggeration to say that the design specifications of the present solenoid device fall within a maturation in a sense from this point of view.
In the various electromagnetic operated valves which perform a simple ON/OFF operation of the directional controll valve or the like or a proportional exciting operation as in the proportional control valve, a reduction in the time constant of the solenoid coil with a view to improving responsiveness can be realized by decreasing the number of turns. However, in order to allow this coil to produce the same magnetic attraction force as the original coil, an excitation current must be increased in accordance with an ampere-turn (AT) regular principle. When a solenoid coil having 1,000 turns as the number of turns thereof is taken, it is uniformly constituted by two split coils each having 500 turns corresponding to the number of turns equal to one-half the above number of turns. If these split coils are connected in parallel and operated, then the responsiveness is improved. However, a power supply current supplied to a parallel combined coil needs twice in order to obtain the same attraction force as in the case of the solenoid coil having 1,000 turns corresponding to the original number of turns. A power loss and electromagnetic induction noise in wiring and each coil also increase as well as an increase in power load to be borne by each of a drive circuit and a power supply for the solenoid device. Thus, while the use of the solenoid coil reduced in the number of turns is effective in speeding up the operation and improving the responsiveness, a coil that excessively increases in drive current, has been taken as unrealistic in terms of practical use.
The solenoid device for the ON/OFF-operation such as the directional controll valve or the like in particular needs to supply a relatively large excitation current in order to exert a sufficient magnetic attraction force on the movable core away from the fixed core in an excitation initial state. However, only a relatively low current value for merely holding the movable core in an attracted state is needed after switching of the valve, and wastage of power cannot be ignored when excitation is continuously carried out with the same excitation current. Therefore, there has heretofore been known a contrivance for inserting a resistor into a coil in series to thereby reduce an excitation current when a certain time has elapsed. However, it is also accompanied by a drawback that since power consumed by the resistor is caused to escape as heat, the effect of performing power saving as viewed from the power supply side is not so obtained, and when such a time limit operation is performed through the use of a semiconductor device such as a transistor or the like, a semiconductor device large in power capacity is needed.